Gasification of carbonaceous solids



Oct 6, 1953 E, H. REICHL ET AL GASIFICATION OF CARBONACEOUS SOLIDS Filed April 5,

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ORNEY Patented Oct. 6 1953 Eric H. Reich],

Mount Lebanon, and Robert V. Sanford, Bethe! Township,

Allegheny County,

Pa., assignor's to Bittsburgh'Consolidation Coal Company, Pittsburgh, Pa., a corporation of Pennsylvania Application April 5, 1948, Serial No. 19,098

1 Claim.

This invention relates to methods and apparatus for effecting complete'gasification of carbonaceous solids, particularly lign'ite, oil shale, bituminous coals, or solid carbonaceous products derived therefrom.

The primary object of the present invention is to provide an improved method and apparatus for converting carbonaceous solids substantially completely to gases useful either as fuels or in the synthesis of liquid hydrocarbons.

Another object of this invention is. to provide an improved method and apparatus for reacting carbonaceous solids with steam and oxygen to yield gaseous products, particularly carbon.

ceous solids are converted to gaseous products by react ng preheated carbonaceous solids with my gen and preheated steam. We have discovered that the steam and the carbonaceous solids supplied to the gasification zone may be preated to high temperatures in an apparatus which is simple in form and economical in operation and which does not involve the use of the cumbersome and costly heat exchangers frequently proposed in the past.

Our invention provides for a vesel in which a fluidized bed of the carbonaceous solids is-maintained by means of steam which, as introduced into the vessel, is at a relatively low temperature. Associated with this vessel is a combustion zone through which a portion of the car'- bonaceous solids from the vessel is circulated along with air whereby a part of the circulating solids is burned. The heat of combustion raises the temperature of the circulating solids which are thereafter returned to the bed of solids contained in the fluid vessel. 7 The rate of circulation of the solids through the combustion zone and the amount of combustion therein. are regulated so as to produce the desiredtemperature in the fluid bed. As a result of this ele- 'vated temperature in the fluid vessel a certain amount of distillation of the carbonaceous solids therein may take place. These vaporous products along with the steam, which is now at the same elevated temperature by virtue of having passed through the hot fluid bed, are conducted to the gasiflcation zone or vessel. Concurrently a portion of the hot carbonaceous solids is drawn on the fluid vessel and is likewise conducted to the gasiflcation zone. To supply the additional heat required to effect complete gasification of the carbonaceous solids oxygen is introduced into 'the'gasification zone. The final gaseous products and ash are separately removed from the gasifl cation zone.

In the preferred embodiment 'of our invention, it is desired to convert carbonaceous solids, particularly bituminous coal, to a gaseous mixture whose principal constituents are carbon monoxide and hydrogen for use in the Fischer-Tropsch process for making liquid hydrocarbons. In this embodiment, we prefer to start with a carbonaceous solid which has been at least partially distilled to effect removal of condensabl'e vapors such as tar which is of value as liquid fuel and as a source of chemicals. The previously distilled solids are raised to a temperature between 1400" F. and 1800 F. in the fluid vessel preheater. The steam and. vaporous products which are of low molecular weight because of the extremely high temperature in the fluid vessel are then introduced into a gasification chamber along with the hot previously distilled solids at the same temperature and with the necessary oxygen.

The precise type of gasification chamber employed incur invention is not material thereto except it is essential that it be adapted to operate at temperatures in the neighborhood of 1900 F. and above. Powdered fuel burners of the Kopp'ers or VortexCombustor types are eminently suitable and for purposes of illustration only the former will be described. In this type of burner, the hot carbonaceous solids first contact the oxygen which is insuflicient to eifect complete combustion of the solids but is suflicient to raise the temperature thereof several hundred degrees. The hot products then are reacted with the preheated steam whereby a mixture of gases is produced which is mostly carbon monoxide and bydrogen. In such a system, not only is the product eminently suitable for use. as synthesis gas in the Fischer-Tropsch process but also the amount of oxygen, which is an expensive reactam, is, reduced to a minimum. In viewofthe, desirability of supplying synthesis gas to the Fis- 2,es4,ee4. p A

cher-Tropsch process under pressure, we provide means for operating our apparatus under pressure. The temperature established in the gasification chamber also generally is sufiiciently high to eifect slagging of the ash produced where separation of gas and ash is facilitated.

Other details, objects, and advantages of the invention will become apparent upon reference to the following description of a preferred embodi-v ment thereof.

In the accompanying drawing we have shown a schematic showing of the apparatus by the use of which the invention may be practiced and have illustrated a present preferred method of practicing the invention.

Referring to the drawing, numeral l designates a gasiflcation chamber wherein finely divided preheated carbonaceous solids are converted to gas by reaction with oxygen and preheated steam. The preheat is supplied to the steam and carbonaceous solids in a preheating vessel indicated by the number l2.

A conduit it serves to conduct steam and carbonaceous solids to the vessel l2, the solids being fed into the conduit it from a hopper it by means of screw feeder it or similar device. Within the vessel 2 a bed of solids i9 is established.

Leading from the lower end of the bed of solids I9 is a conduit 26 for conducting solids from the bed id to a combustion tube 28. A control element 3b is provided in the line 28 to regulate the flow of solids therethrough. Air is supplied to the combustion tube 28 through a conduit 32 impelled by a pump (it.

The combustion tube 28 is directly connected to a cyclone separator 36 by a conduit 38. The Separator has a leg it extending into the bed of solids I9. Leading from the top of the cyclone separator is a tube 42 which extends through the wall of the vessel l2 and continues as conduit 44 for carrying flue gas. This conduit 4 is arranged with respect to the air conduit 32 to provide a heat exchanger 15 and with respect to conduit id to provide a heat exchanger 46. A conduit dl connects conduit 44 with a turbine expander 58 which drives the blower as by means of a shaft 49.

A conduit 50 connects vessel 2 at a point above the level of the bed 19 with the gasiflcation chamber H] for conducting steam thereto. Another conduit 52 serves to carry solids from the bed l9 to the chamber It. A control element 54 is disposed in the line 52 for regulating the flow of solids therethrough. A conduit 56 is arranged to conduct oxygen from a source of oxygen 58 to the gasifioation chamber lEl. Connecting the oxygen plant 58 with the steam line It is a conduit St! for providing steam needed in the operating of the plant.

The gasification chamber Iii is provided with an outlet 62 for ash produced in the gasification reaction. The gaseous products of the reaction are conducted away by a conduit 64. This conduit is arranged with respect to the conduit M to provide a heat exchanger 66 which in conjunction with heat exchanger 58 serves to convert to steam the water introduced into the conduit is by a pump 68.

The operation of a preferred embodiment of our invention will now be described. While the invention is applicable to the gasification of any carbonaceous solid, it is particularly applicable to the treatment of oil shale, lignite, bituminous coals and products derived therefrom. We prefer to employ previously distilled coals, i. e., chars, cokes or semi-cokes from which volatile matter has been distilled, preferably at low temperature, in order to derive the benefit of the valuable components of the vaporous products. Accordingly, the operation of the present invention for purposes of illustration only will be described as applied to a distilled coal which for convenience we shall call coke, this coke being produced as a result of the low temperature carbonization of a high volatile Pittsburgh seam coal.

Coke in finely divided form is fed from the hopper It by means of a screw feeder it into the conduit l4 where it is picked up by steam and carried to the preheater vessel E2. The steam is produced from water, which is pumped into conduit It by a pump 68, by means of heat exchangers 46 and 65 to be described more fully below. The flow of steam and coke into vessel 12 is regulated in the well-known manner to produce a fluidized bed [9 of coke, with steam being the sole fluidizing agent.

The temperature of the fluid bed It is maintained in this preferred embodiment within the range 1400-1800 F. by means of heat supplied by burning a portion of the coke. This is accomplished by removing coke from the bed 19 through a conduit 26, the amount being regulated by a valve or constriction 3t, and burning a portion of this coke with air in the combustion tube 28. The air is impelled to the combustor through conduit 32 by means of pump 34. It is preferably preheated by being circulated in heat exchange relation with hot flue gas as indicated by heat exchanger 46. The combustion of a portion of the coke in the upfiowing mixture of air and coke in the tube 28 produces hot flue gas and hot coke. These are separated in the cyclone es, the hot coke being returned to the bed [9 and the hot flue gas being vented through conduits c2 and 34. The circulation of coke through the side-arm combustion tube 28 and the flow of air as well are regulated in such a manner that the temperature of the bed l9 can be maintained at any desired value but preferably in this example is between 1400 and 1800 F. Since the steam passes through this hot bed of coke, it too, attains the same temperature.

In the preferred operation of our invention, the entire system is under pressure. This is accomplished by passing a portion of the hot flue gas coming from the cyclone separator 36 through conduit 41 and exchanger 45 into turbine expander 48 which is directly connected to blower 34. High pressure air is then forced by the blower 34 into the combustor 28. This high pres sure extends through the entire system including both the preheater and gasification chamber because of the open communication therebetween. Hopper [6 should in this case be of the locking type and adapted to supply the solids to the system without loss of pressure therein.

Hot finely divided coke from the outer zone 24 of vessel I2 and hot steam from above bed 39 in the same vessel are conducted in any suitable manner through conduits 52 and 58, respectively to the gasification chamber it. The flow of not coke may be controlled by a valve or constriction 54. Oxygen is supplied to the reaction chamber 10 from an oxygen plant 58 in order to provide the additional heat required to promote the reactions between the steam and the coke.

As stated previously, the particular type of gasi fication chamber employed is not a part of the present invention. However, for purposes of i1- lustration we have shown a powdered fuel burner of the Koppers type. In this burner, the coke is first reacted with a deficiency of oxygen to raise the temperature of the coke. The hot steam then reacts with the hot reaction products of the oxygen and coke to produce principally carbon monoxide and hydrogen. The temperature maintained in the burner is of the order of 1900- 2500 F. if non-slagging of the ash is desired and 2500-3000 F. if slagging of the ash is desired.

The hot gaseous product which is suitable for use in the Fischer-Tropsch process is conducted through conduit 64 to heat exchanger '66 where in conjunction with the heat exchanger 48 heat obtained from the flue gas of vessel I 2 and the syn thesis gas from chamber In serves to convert water in line H to steam. The synthesis gas is then led to any convenient place, preferably directly to a Fischer-Tropsch unit. The ash from chamber I0 is drawn off through outlet 62.

The shape and design of the preheter I2 may also vary, bearing in mind that for the purposes of this invention it is essentially a heat exchange device for preheating solids and steam with the minimum of change in the character of the solids. Accordingly, the bed of solids is preferably shallow in depth so that the time of contact of steam with solids is just sumcient to raise the temperature of the steam to that desired.

We wish to point out that in the claim whereever the term coal is employed it is intended to include all ranks of coal, lignite, bituminous, and anthracite as well as carbonaceous products derived therefrom.

According to the provisions of the patent statutes, we have explained the principle, preferred construction, and mode of operation of our invention and have illustrated and described what we now consider to represent it best embodiment. However, we desire to have it understood that, within the scope of the appended claim, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

The method of gasifying carbonaceous solids which comprises passing steam into a bed of finely divided carbonaceous solids under fluidizing conditions, withdrawing a portion of said carbonaceous solids from said fluidized bed, conveying said withdrawn portion to a separate combustion zone, burning a part of said withdrawn portion in said combustion zone with air to thereby raise the temperature of said withdrawn portion, conveying the heated solids from said combustion zone back to said fluidized bed, the temperature and amount of said heated solids returned to said fluidized bed being such that a temperature between 1400 and 1800 F. is established and maintained in said fluidized bed, withdrawing hot efiiuent gas, including unreacted steam, and hot carbonaceous solids separately from the fluidized bed, separately conducting said hot efiluent gas and said hot carbonaceous solids to a steam-carbon gasification zone, adding oxygen to said hot carbonaceous solids prior to entry into said gasification zone in an amount insufficient for complete combustion of the solids but sufficient to raise the temperature of the gasification zone above 1900 F., reacting the solidsoxygen reaction mixture with said efiiuent gas in the gasification zone under nonfluidized conditions, whereby substantially all of the carbonacely carbon-free ash, and then recovering the gaseous solids are converted to gas and a substantialous products from said gasification zone.

ERIC H. REICHL.

ROBERT V. SAFFORD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,924,856 Heller Aug. 29, 1933 2,420,145 McAfee May 6, 1947 2,436,938 Scharmann et al Mar. 12, 1948 2,462,366 Davies, Jr., et al Feb. 22, 1949 2,482,187 Johnson Sept. 20, 1949 FOREIGN PATENTS Number Country Date 413,130 Great Britain July 12, 1934 OTHER REFERENCES Haslam et al.: Fuels and Their Combustion, 

